1. Field of the Invention
The present invention relates to an optical-pickup-adjustment optical disk used when an optical pickup device of an optical disk apparatus is adjusted, a method of adjusting an optical pickup device using the optical-pickup-adjustment optical disk, and a method of producing an optical pickup device using the method of adjusting an optical pickup device.
2. Description of the Related Art
A compact disc (CD), in or from which information is recorded or reproduced using a red laser beam having a center wavelength of 0.78 μm, and a digital versatile disc (DVD), in or from which information is recorded or reproduced using a red laser beam having a center wavelength of 0.65 μm, are put into practical use as optical disks. Further, a “blue laser optical disk” such as a High-Definition DVD (HD-DVD) and a Blu-ray disc, in or from which information is recorded or reproduced using a blue laser beam having a center wavelength of 0.405 μm, is started to be in a practical use.
Further, a multilayered optical disk including a plurality of information recording layers is standardized in the DVD standard or the Blu-ray disc standard in order to implement higher density recording. In general, since an optical disk includes a transparent protective substrate on a side of laser beam incidence, the protective substrate of a multilayer optical disk has different thicknesses in a region of a shallow information recording layer which is near the surface of the protective substrate and another region of a deep information recording layer which is far from the surface of the protective substrate. For example, the Blu-ray disc standard prescribes that a distance between a shallow layer near the surface and a deep layer far from the surface is 25 μm, a thickness of the protective substrate in a region of the shallow layer is 75 μm (an average value), and a thickness of the protective substrate in a region of the deep layer is 100 μm (an average value).
When a laser beam converged by a lens enters the protective substrate, spherical aberration occurs in accordance with a thickness of the protective substrate. Since the spherical aberration sometimes causes a trouble in recording or reproducing a signal in or from an optical disk, an optical system including a lens and a light detector is designed in such a way that the spherical aberration of an optical pickup device becomes the smallest.
As has been described, since the spherical aberration depends on a thickness of the protective substrate, an optical pickup device compatible with a multilayer optical disk needs to have a function of adjusting the spherical aberration by itself. For example, there is a proposal of an optical pickup device that can adjust the spherical aberration by moving a collimator lens along an optical axis for converting a laser beam ejected from a semiconductor laser to a substantially parallel light beam (e.g., see Patent Document 1).
Patent Document 1 is Japanese Patent Application Kokai (Laid-Open) Publication No. 2005-327395 (page 7, FIG. 2).
In the optical pickup device disclosed in Patent Document 1, it is required that a collimator lens be moved only in a direction of an optical axis in an ideal case. However, a movement mechanism of a practical collimator lens normally has “play” and “looseness”, and also has an arrangement error in component members of the movement mechanism. Therefore, when a collimator lens is moved by the movement mechanism in a direction of the optical axis, a little displacement of the collimator lens occurs in a different direction from a direction of an optical axis. When the undesired displacement of the collimator lens occurs in the different direction from the desired direction of the optical axis, a positional relationship between a laser beam reflected from an optical disk and a light detector receiving the reflected laser beam to detect it, deviates from a desired positional relationship. As a result, the conventional optical pickup device has a problem that a detection signal output from the light detector varies due to the movement of the collimator lens.